Project summary ? RP2 Non-typhoidal Salmonella (NTS) such as Salmonella Typhimurium and Salmonella Enteritidis generally cause self-limiting gastroenteritis. NTS is estimated to cause 94 million cases and 155,000 deaths worldwide each year. Whereas the incidence of disease caused by other important enteric pathogens have been reduced consequent to interventions initiated by FoodNet, the incidence of Salmonella disease in the U.S. has remained the same and was reported to be 7452 infections per 100,000 in 2014. NTS disproportionally affects the very young and the elderly. Our overall goal is to develop vaccines to provide broad protection against NTS disease. This proposal seeks to build on our previous work where we have developed live attenuated S. Typhimurium, S. Enteritidis, S. Newport and S. Virchow vaccines. The main goals of this project are to show that our live vaccines can provide broad protection against NTS gastroenteritis and that they will be effective in potential target populations. To achieve these goals, we propose the following aims: Aim 1. Determine whether candidate live attenuated non-typhoidal Salmonella (S. Typhimurium [serogroup B], S. Enteritidis [serogroup D], S. Virchow [serogroup C1] and S. Newport [serogroup C2]) vaccines can protect against gastroenteritis; Aim 2. To identify a mechanistic or non-mechanistic correlate of protection for our candidate live attenuated S. Typhimurium vaccine; Aim 3. To predict performance of live attenuated NTS vaccines in target populations; Aim 4. To evaluate a multivalent formulation of live attenuated Salmonella vaccines and determine whether elicited antibodies are effective against clinical strains including antibiotic-resistant Salmonella. At the conclusion of this project, we anticipate that we will have shown that our candidate NTS vaccines can mediate protection against gastroenteritis and we will have identified mechanistic and non-mechanistic correlates of protection. We also anticipate that we will have determined whether our live oral vaccines produce antibodies that recognize currently circulating antibiotic-resistant strains. Finally, we will have shown that our vaccines are immunogenic in target populations. If we are successful, these results will pave the way for initiating future Phase 1 clinical trials.